Archive for the ‘Ryan’s Research’ category

The 4th MSL Landing Site Workshop: Day 2 – Mawrth

September 29, 2010

Holy cow. Today was jam-packed with interesting stuff about Mawrth Vallis, Holden Crater and Eberswalde Crater! I took tons of notes, and I will try to use those to assemble a coherent picture of what was presented and discussed today. But if you’re too impatient to wait for me to work through those and post the more coherent summary, here are the notes in their raw and unedited form. Read them at your own risk, they’re full of jargon and typos and abbreviations! I’ll update that file tomorrow with tomorrow’s notes too.

In the meantime, I’ll start to translate those notes, starting with the first site on the table this morning: Mawrth Vallis. Joe Michalski started off the day with an overview of Mawrth emphasizing some of the key points about the landing site. Of course the obvious draw for Mawrth is that it is the best exposure of clay minerals on Mars. Clays form in wet environments and are good at trapping organics, so they are very desirable for MSL.  Joe (and subsequent speakers) also emphasized that Mawrth also has morphologic diversity and that it is an extremely old portion of the martian crust. Joe also pointed out that the fact that we see lots of clay minerals at Mawrth is not because Mawrth is unusual for early Mars. It’s much more likely that much of the early crust has similar minerals, but Mawrth is the best exposure.

The colors in this HiRISE image correspond to changes in the mineralogy. A similar stratigraphy is seen throughout Mawrth and the surrounding region.

The next talk was by Janice Bishop who summarized the mineral diversity in the site. She showed a bewildering number of spectra from Mawrth, and drove home the fact that the mineralogy observed occurs in the same stratigraphic order all over mawrth and all over much of the Arabia Terra region on Mars, supporting the idea that understanding Mawrth would teach us about a huge section of the planet. One of the interesting things that Janice and others showed is that these compositional layers are observed in some layered rock in the floor of Oyama crater, the huge crater to the west of the ellipse. This is interesting because it is thought that the rocks in the ellipse are older than Oyama, and obviously the rocks filling Oyama are younger. The fact that they show the same mineral stratigraphy suggests that the related alteration came after the physical deposition of the rocks.

After Janice’s talk, Eldar Noe Dobrea gave an overview of the morphology of the site. He showed a lot of nice HiRISE images of the site, and also gave examples of possible models for how the rocks at Mawrth were deposited, including impact ejecta, airfall, lakes and rivers, or an ocean. Eldar also showed a map of the ellipse that was completely peppered with markers indicating that he had observed layers. This was a contentious issue later in the day because Dawn Sumner, a sedimentary geologist who mostly studies the earth, gave a presentation saying that she didn’t see any convincing layering in the ellipse. Eldar also did something that John Grotzinger specifically said was very useful: he listed some of the thinks we don’t know about the site. In particular, we don’t know the origin of the clay-bearing rocks or the clays themselves. We also don’t know the amount of water that eroded the landscape or its pH, and we don’t know much about the dark unit that caps the stratigraphic sequence at Mawrth.

Another pretty HiRISE picture of Mawrth, showing some of the detailed surface textures.

Next up Damien Loizeau gave a nice talk about what we would do on the first day, month and year at Mawrth, and then Jean-Pierre Bibring gave a concluding presentation. Bibring emphasized the great age of the Mawrth Vallis rocks, pointing out that on earth rocks as old as Mawrth do not exist intact. All we have to work with are mineral grains preserved in younger rocks. So by going to mawrth we might actually learn a lot about Mars as well as about the conditions on very early earth.

Finally, as I mentioned above, Dawn Sumner gave a presentation based on her studies of the physical stratigraphy at Mawrth. She suggested that most of the features at Mawrth are due to cratering and that many of the “layers” are either fractures in the rock from impacts, or are not traceable for more than a few hundred meters at most. (Dawn also showed some very cool movies illustrating some of her points, using a new 3d visualization program that some of the other folks at UC Davis have developed called Crusta.)

After Dawn’s presentation there was a discussion period for Mawrth Vallis. One of the points that came up a few times is that the physical stratigraphy that Dawn was looking at is different from the mineral stratigraphy that seems to show more Al-rich clays above more Fe and Mg-bearing clays. There were also comments suggesting that it may actually be desirable to go to a complex ancient cratered surface precisely because it is confusing and there is no good terrestrial analog for us to study here  on Earth. Finally, there was a question about the abundance of clay minerals. In mixing models, Francois Poulet claims to see up to 60% clay minerals at Mawrth, based on OMEGA visible and near-IR data. But in thermal IR observations don’t see nearly that abundance. Steve Ruff, an expert in the thermal IR, said that TES does see some evidence of alteration but not at that sort of abundance. One expanation that he suggested is that the phyllosilicates might be poorly crystalline, so that VNIR observations see something but thermal IR doesn’t.

At the end of the discussion of Mawrth, I felt a lot better about the site than I did before going in. There is clearly a lot of good stuff to do there, and it has a couple of undeniable advantages: it is clearly the oldest site, and you get to land on your primary target. But I’m also concerned by what I hear from terrestrial geologists who are very concerned about how much Mawrth would actually tell us about the habitability of Mars. Yes, it has spectacular phyllosilicates, but it’s not clear that they would trap any organics since we don’t know what the depositional setting was. I think despite this uncertainty, if you polled the community, Mawrth would be one of the top two sites.

4th MSL Landing Site Workshop: Day 1

September 28, 2010

It has begun! Today was the first of a three day workshop in which the Mars science community (not just those directly involved in the MSL mission) gathers together and hashes out what we know and what we don’t know about the four finalist MSL landing sites.

For me the week actually started yesterday at the MSL team meeting, where we got lots of updates on the various aspects of the mission. Unfortunately, I don’t know how much of what I heard yesterday is safe to share with the world. Having been scolded before for sharing too much here I will just say that it’s really exciting to see all the pieces of the puzzle coming together.

Today, and for the rest of the week, everything is fair game to share with you, so I will do my best! Emily Lakdawalla will also be blogging parts of the meeting, so I’ll also point you to her posts about the meeting as they go up. In fact, you should go check out her introductory post right now. You might also want to refresh your memory about the four sites by reading this summary.

Today started off with some overview talks from the project manager Mike Watkins and project scientist John Grotzinger. Mike showed some awesome pictures of MSL (aka Curiosity), which is really starting to look like a rover. A jaw-droppingly huge rover. Watkins also had some nice analogies to go along with his pictures to convey just how huge Curiosity is. Remember the little Sojourner rover? It could just about use MSL’s wheels like hamster wheels. MSL is also really tall: its mast cameras could look Shaq straight in the eye, and its gigantic arm is so long it could almost dunk!

Curiosity is a huge machine. Note that the giant blob of instruments are not yet mounted on the arm in this photo.

I’m going to cheat and share a little of what I heard yesterday because this arm is just amazing and they used another good analogy. The instrument package at the end of the arm is huge: about 35 kg. You can picture this as something the size and weight of a lawn mower mounted on the end of a seven foot arm. The arm itself weighs 70 kg, and it is strong enough to dead lift that lawnmower even when the arm is fully extended. The MER rovers weigh 172 kg, the MSL arm weighs 105 kg. It. Is. Huge.

It finally sank in when I saw the presentations yesterday and today just how massive this rover is.

Anyway, back to today’s presentations. After the introduction, there were a series of talks about the preservation of biosignatures. One of the main take home points from these was that context is critically important for detecting and understanding biosignatures. If you understand the geology, you can try to look in places that maximize your chances of finding something. And then if you do find something, you can draw much better conclusions if you know its environment. This sort of argument makes a site like Eberswalde, where the story of a delta deposit in a crater lake is pretty well understood much more appealing than a site like Mawrth, where there are beautiful minerals, but we don’t really know the geologic story. Gale and Holden are both somewhere in between.

After biosignatures, there was a set of presentations about the mineralogy of the landing sites. This started with Frank Seelos unveiling the new and improved website containing a set of CRISM spectral images of the landing sites. You should go check them out: he specifically said that he would love it if we all melted his servers!

An example CRISM map of part of the Mawrth Vallis landing site, showing off the spectacular hydrated minerals in the site.

We also heard from Selby Cull, a graduate student who is attempting to use detailed models to figure out how much of a given mineral is in a sample based on its spectrum. Although it sounds straightforward, this is actually a phenomenally complex problem that planetary scientists have been grappling with for decades. It would be awesome if we could do this, but I’m skeptical.

After Selby, Ray Arvidson gave a talk about tying orbital to surface data at the MER Opportunity landing site and lessons learned that MSL should keep in mind. Bottom line (paraphrased) is that wherever you go, Mars is going to be more surprising and more interesting than we can imagine!

Finally Ralph Milliken shared his results on the compositions of the landing sites based on CRISM observations. It turns out that, using a subtle spectral parameter, you can estimate whether a given clay mineral detection is more or less “evolved” (where evolution could be due to burial or impacts among other things). Ralph also showed some exciting new stuff at Gale crater, including an example of a set of minerals visible in the southeastern portion of the Gale crater mound that looks very similar to the stack of mineral signatures seen near the landing ellipse.

A colorful map of the mineralogy at Gale Crater from Ralph Milliken. Greens are phyllosilicates, blue and magenta are sulfates, red is olivine, and orange is mixed sulfates and clays. The landing site is at the top center of this image, and the rover would ideally drive to the northwestern part of the mound, where there is lots of CRISM coverage.

Finally, after the mineralogy talks were over, we started hearing presentations about the specific landing sites. Gale was up first, and after Ken Edgett summarized the crater’s global and regional context along with some of what you can see within the crater, I gave my presentation showing off the interesting stuff that can be accessed in the ellipse and on a notional traverse up the lower portion of the mound. After me, my adviser Jim Bell presented about the composition of the stuff at Gale, and then finally Dawn Sumner gave a really interesting presentation about how to test some of our hypotheses at Gale Crater.

In the discussion of Gale the inevitable questions came up. One was: how old is the mound? The “problem” with answering that is that we think most of the terrain at Gale was buried and has since been exhumed again. That can totally throw off your estimated ages based on crater counting. The properties of the surface matter can too: some surfaces are hard and erosion resistant, so they tend to have more small craters than adjacent surfaces even if they are younger.The best estimate is that Gale crater formed at the end of the “noachian” period of martian history and the mound formed sometime in the late noachian to early hesperian. The exact timing of these epochs isn’t all that well constrained, but the noachian ended around 3.8 to 3.5 billion years ago, and it’s fair to say that Gale and its mound are about that old.

Three views of Gale crater. Top: An HRSC topographic map of the crater. Middle: A THEMIS thermal inertia map of the crater. Brighter areas are rockier, darker areas are dustier. Bottom: A THEMIS "decorrelation stretch" map, showing variations in color that can be roughly tied to composition. Pink is olivine, blue is dusty. Source: Anderson and Bell (2010)

We also talked about what it might mean if the whole mound is wind-blown grains. It’s certainly possible, but very difficult to tell from orbit. If the grains just filled up a dry crater, that might not be so good for habitability, but the mound is carved by canyons so we know there was flowing water well after the mound material had been deposited and turned to rock. On the other end of the spectrum, the mound might all be wind-blown grains, but those could have been trapped in the crater because it was full of water. As we heard earlier in the day, fresh basaltic sand plus water would provide the chemical energy necessary to support a pretty impressive chemolithoautotrophic (aka rock-eating) biomass.

There was also a lot of discussion of the evidence that Gale was actually buried. Someone asked whether there are any patches of layered material on the crater wall that match the mound layers. There aren’t, but I pointed out that there is a nice outlier of layered material hidden in the dune field 20km west of the mound itself. Ken Edgett reminded people (as he has been doing for 10+ years) that “this isn’t the mars you’re used to thinking about”, that entire regions have been buried and exhumed, and that this can happen without leaving a trace on the underlying surface. He also pointed to Henry crater as a Gale-sized example that does have a mound that matches with material on the walls. The question of why Gale seems to have preserved its huge mound of sediment, but all the other craters nearby did not keep theirs came up, and John Grant suggested that we do crater counting on the nearby craters which we know are older than Gale to see if their surfaces are anomalously young – as if they had been buried for a few billion years.

I also got the question of whether we should try to visit all of the cool stuff that I showed in the landing ellipse if the true goal of the mission is the mound. This is going to be the core question for this mission. At all the sites but Mawrth, you land on cool stuff but your main goal is outside the landing ellipse. The tradeoff between doing the “safe science” right away in the ellipse and sacrificing science early on to be able to make it to potentially more rewarding targets is going to be a huge part of the landing site discussion over the next few months. On Wednesday we are going to hear from some of the engineers and rover drivers about the engineering constraints on the mission, and then the Landing Site Working Group (a small subset of scientists that have been looking very closely at the landing site) will work with the rover drivers to identify the key targets at a given site and the key observations we want to make at those targets. From there, the engineers will come up with a set of potential traverses with detailed estimates of how long each will take. Since all of the sites are safe to land in, I think these estimates will play a major role in finally narrowing down to the final selection next spring.

The 4th MSL Landing Site Workshop

September 24, 2010

Well folks, I’m off to Pasadena to help the Mars community decide where to send its next rover. Long-time readers will recall that i’ve been to a couple of these things before and they’re always fascinating. I was going to post a reminder of what the four finalist sites are, with pros and cons and all that, but it turns out I don’t have to! My friend Lisa Grossman, a former Cornell astronomy major, is now a science writer for Wired! She interviewed me and my adviser earlier this week and put together a nice article summarizing the sites. I’m quoted in it quite a bit, so rather than repeat the same stuff, I’ll just point you over to her piece.

There are a few points of clarification that I should mention. First, the article says that MSL is searching for life, and that’s not really true. MSL is searching for signs of habitability. Obviously finding life would be a pretty good sign! But habitability is broader than just the search for life or even the search for organic molecules. Evidence for habitability could come from the texture of a certain rock telling us that it was deposited in water, or from the detailed chemistry revealing that the minerals in the rock could only form in benign liquid water.

Also, she’s right that some of the clays at Mawrth are kaolinites, which tend to form on earth in tropical soils. But to clarify, I don’t think anyone is saying that the huge amount of kaolinite clays at Mawrth are the result of tropical conditions. They do suggest that there was a lot of water involved though, which is why Mawrth is so interesting.

A final clarification: in the article, it mentions that it will take “several days of hard driving” to get to some of the go-to sites, where the really interesting stuff is outside the ellipse. If it were several days, that would be no big deal. It is going to be more like a year or two. A lot of people are really nervous about landing, only to have to buckle down and drive drive drive to get to the main target of the mission. Of course, all of the sites have good science to do in the landing ellipse, but that is a blessing and a curse for a go-to site. On the one hand, you get some results early on in the mission, but if you don’t have a lot of discipline, you can spend all your time staring at the rocks at your feet and never get to go climb the mountains in the distance.

With that, I’ll let you go read the article. You can also check out my old blog posts about the sites from the last time one of these workshops was held (Gale, Holden, Mawrth and Eberswalde). I’m going to do my best to take notes and blog about the meeting, and Emily Lakdawalla of the Planetary Society will be there for part of the meeting as well. We’ll do our best to keep you informed!

PS – You should totally check out the comments on the Wired article, where someone calls me out for saying that there was water on Mars and says that we Mars scientists are either stupid or have ulterior motives. Someone hasn’t been paying attention to every press release about mars for the past decade or so.

Gale Crater Geomorphology Paper – Published!

September 16, 2010

Big news folks! The huge paper that I’ve been working on for the last couple years is finally, unbelievably, published! Even better for you, it is published at the Mars journal, which is an open-access journal. Just head on over and you can download all 53 pages of pure, distilled Science!

In case you don’t want to wade through that many pages (and almost as many figures) of Mars geomorphology jargon, I’ll summarize here.

Gale Crater is a large (155 km diameter) crater that sits just south of the martian equator on the boundary between the rugged, cratered highlands to the south and the smooth plains of the northern hemisphere. Gale is special because it’s not just a big hole in the ground: in the middle of the crater is a vast mountain of layered rocks that towers nearly 6 kilometers above the crater floor. As I’ve mentioned before on this blog, geologists love layers, because they are formed in the rock record when something changes. So the Gale Crater mound is a giant record of the changes that have taken place on Mars since the crater formed3 or 4 billion years ago. This fascinating stratigraphic section has evidence of water-bearing minerals like clays and sulfates, and the detections of these minerals seem to follow certain layers, so the hope is that those layers were deposited during a time when Mars was more habitable. That’s why Gale Crater is one of the four finalist landing sites for Mars Science Laboratory!

Even though a lot of people knew that Gale had this interesting mound, not a lot of work had been done on the crater, so in an effort to help the Mars community learn all we can about the geology of this possible landing site before making the decision whether or not to land there, I dove into the image data for Gale crater. I started with the Context Camera (CTX), making a huge mosaic covering the whole crater. I used that mosaic to map out easy-to-map features like sand dunes and branching channel networks.This was scientifically useful because it shows that there are lots of channels formed by water flowing into the crater, but it was also a good way for me to learn to use the mapping software ArcGIS.

After that, I spent a while working on determining the orientation of the layers in the mound using a digital elevation model based on CTX images. This work was also educational, but ultimately after showing it to several colleagues I found it was drawing criticism and wasn’t telling us a lot about the mound, so that was cut from the final paper.

I moved on and pored over the various HiRISE images of the potential landing site and the mound, identifying “units” based on their appearance in HiRISE, supplemented with CTX, thermal inertia data from THEMIS, and spectral data from CRISM. In doing so, I was able to put together a more detailed picture of what a rover might encounter if it landed on the crater floor and drove up the mound.

Three examples of inverted channels in the proposed MSL landing ellipse.

The landing site is centered on a fan of material that extends from the northwestern wall of the crater and ends a few kilometers from the base of the mound. Looking closely at the fan, it turns out that about two thirds of it is mantled with what looks like dust or soil, but the final third, closest to the mound, has been stripped bare, exposing a bunch of fractured layered rock. That’s interesting in an of itself, but the fan isn’t the only thing in the landing ellipse. I also found some examples of inverted channels: riverbeds that were resistant to erosion and ended up as mesas when the surrounding land was stripped away. There are also patches of a unit that I called the “mound-skirting unit” within the ellipse.

This mound-skirting unit is found all around the crater and tends to be erosion resistant, forming mesas. It also looks like it might be related to flowing water in some places: chains of mesas made of this unit extend across the floor from channels and fans on the crater wall. But elsewhere, there are parallel ridges in the mound-skirting unit that might be the remnants of ancient dunes that were petrified. One notable patch of the mound-skirting unit is partway up on the northwest side of the mound, right at the end of a channel that was carved into the layers of the mound and later filled with debris. This has been referred to as a fan, and if I had just looked at it without context I would have called it a fan too! But it has almost the exact same texture as the mound skirting unit nearby. My interpretation for this was that the original fan is mostly eroded away, but because there was a fan sitting on top of the mound skirting unit in this spot, it was protected from erosion so it remains as a mesa at the end of the filled channel.


Examples of erosion-resistant ridges on the Gale mound that might be due to water percolating through the rocks.

Another interesting thing that I noted about the surface of the lower mound is that there are cracks all over the place that look like they are resisting erosion, becoming lattices of ridges. This could happen if water was flowing through the rocks, cementing the material near the fractures and making them last longer than the un-cemented surrounding rock. These fractures occur in a part of the mound that shows hydrated sulfate signatures in CRISM, so there is some supporting evidence that water was involved.

I also looked at some of the material near the top of the mound, far beyond where MSL is likely to reach even with multiple extended missions, and I’m really glad I did. One of the big questions about the Gale mound is what type of rocks it is made of. It’s a lot nicer for habitability if you can say for sure that rocks formed in a lakebed instead of a desert, but it’s frustratingly difficult to tell the difference with orbital data. The upper part of the Gale mound might be an exception though: If you look really carefully, in some of the HiRISE images there is a strange “swirly” looking pattern that I interpreted as a cross-section through ancient sand dunes. If true (and there are certainly other possible explanations), this tells us that the upper mound was once a location where sand collected to form dunes, meaning it was probably a low point rather than a high point.

Examples of the weird texture in the upper mound that might be evidence that these rocks were once sand dunes.

The idea that Gale has been buried isn’t a new one, and after looking at the geology of the mound, I think it has actually been buried and unburied several times. The lower layers of the mound have deep gorges carved into them and craters on the surface, suggesting that they’re old, and that they were already eroded into a mound back when water was eroding things on mars. Above the lower mound is the upper mound, which looks like it was deposited separately, possibly much later. There is a channel in the lower mound that disappears beneath the upper mound to mark the “unconformity” between these two units. This means that just because I found what I think are petrified dunes in the upper mound, the lower mound isn’t necessarily the same stuff.

There’s lots more in the paper, but those are some of the key points. In a couple weeks I’ll be presenting at the MSL Landing Site workshop, where people who have been studying the four potential landing sites will share their results and the whole Mars community will argue and try to decide which site we should land at. These meetings are always exciting, and I’ll do my best to blog about the meeting here. The final decision won’t happen at the upcoming meeting, but it will be interesting to see if any sort of consensus starts to form. (don’t hold your breath!)

HP dv6t Select Edition Notebook Review: First Impressions

July 24, 2010

Please excuse me while I geek out about my new laptop…

My work now involves some really significant number crunching, to the point that I was regularly using all the CPU and RAM of my previous laptop, and was then struggling to get anything else done while the calculations were running. And then they would crash. It also helps that I will soon need to renew the license on one of the programs that I use, and the student price is only available for a given CPU once. And of course, there’s a game coming out on Tuesday that I really wanted to be able to play.

I decided from the outset that I was going to aim for a high-end system this time. I spend a ridiculous amount of time in front of my laptop, for both work and fun, so I wanted a quality machine. After lots of web-searching and comparing, I decided on the HP dv6t Select Edition. It had impressive specs, and there was a $400 coupon to sweeten the deal. Here are the full stats:

  • Processor: Intel Core i7-840QM processor (1.86GHz, 8MB L3 Cache) with Turbo Boost up to 3.2 GHz
  • Windows 7 Home premium 64 bit
  • Hard Drive: 500 GB 7200 RPM
  • RAM: 8 GB
  • Screen: 15.6″
  • Resolution: 1366×768
  • Approximate weight: 5.5 lbs
  • Graphics: 1GB ATI Mobility Radeon(TM) HD 5650 Graphics + HDMI and VGA ports – For Quad Core Processors

The computer arrived on Thursday, so I’ve had a little time to get it set up and get used to it. Here are my first impressions:

First of all, this is the sexiest computer I’ve ever owned. I really like the (mostly) metallic case and the subtle texture on the lid and hand rests. I saw somewhere that similar HP designs had a “pinkish” hue to the metal, but the dv6t SE definitely does not.The computer also feels solidly built, with no “wiggle” in the screen hinges and no flexing when picked up by the corner.

Click for a closer view of the lid texture.

Also, I love the “chiclet” keyboard. It just feels good to type things on it, and it is big enough that I don’t feel cramped at all. If you’re considering this laptop, I highly recommend paying the $25 more for the backlit keyboard. I didn’t realize how useful this feature would be, but I have used it quite a bit.

I do have a few complaints. The biggest problem is the track-pad. For some reason, HP decided to forgo having separate buttons to click and instead made the lower left and right corners of the track-pad clickable. This would be ok, except that those areas also still work as a tracking surface. When I’m using the track-pad I like to have one hand pointing and the other clicking, but this doesn’t work so well when the buttons also act as the pointing surface. Also, you have to push the corner “buttons” down a lot harder than I’d like. The track-pad is also supposedly multi-touch sensitive. I haven’t played with this feature much, but have found it to be pretty unresponsive and therefore useless for scrolling around web-pages and documents.

The trackpad is the worst feature. Click to see its weird all-in-one buttons and the nice texture of the hand-rests.

Basically what I’m saying is that if you get this computer, be prepared to use a wireless mouse. That’s what I normally do anyway so the trackpad is not that big a deal for me.

Another very minor complaint is the row of keys on the far left side of the keyboard. I am used to the control button being the lowest left one, but on this laptop, to the left of ctrl is a button that brings up a calculator program. I find myself occasionally hitting the wrong button and having a calculator pop up instead of, say, copying text with ctrl+C.

One other downside is that it does come with quite a bit of HP crap-ware. But most computers come pre-loaded with software that you’ll never use. Once you get the worst offenders uninstalled or at least turned off, it’s fine.

I really like the keyboard, though I sometimes hit the calculator button instead of Ctrl.

Other factors that might be a problem for some users are heat and battery life. I sprang for a very fast Intel i7 Q840 processor, which puts out a lot of heat when it is working hard, and eats up battery life. I haven’t formally tested the battery, but I wouldn’t count on more than 2 hours. Again, that’s not a big deal for me because I almost always use my laptop near an outlet. And my previous laptop’s battery life had dwindled to about 7 minutes, so this is luxury for me! There is a larger battery than the one I have, so there’s always that option if you’re considering this laptop and want more battery life. The computer itself is very sleek but I was surprised at how chunky the power adapter is. Both the cord and the brick are pretty hefty. Again, this might be an issue for some but not a big deal for me: I’m used to my slightly-heavier Toshiba with a less-bulky AC adapter so the total weight will be similar.

Here's a close-up of the light-up HP logo and texture on the back.

Coming back to heat: yes, this computer runs hot. For normal use it’s warm but not uncomfortable to use on your lap, but if you’re doing anything CPU-intensive, this computer (and any notebook really) should be on a hard surface to allow plenty of air-flow. When I was running work programs, it got mighty toasty.

But holy cow is it fast. It’s noticeably zippy at basic usage tasks, like installing and opening programs, but what really blew me away was using it for work. Not only is it faster, but since I got the 64-bit Windows 7 with 8 gigs of RAM, it easily was able to load my entire dataset for work without breaking a sweat. My previous laptop had to break the data into chunks and half the time would crash if I tried to load too much of it at once.

Bottom line, I am really loving this computer. It looks and feels really nice and has awesome performance to match. The only major downside is the trackpad, and I typically use a mouse anyway so it isn’t a big deal for me. There are some other nitpicks, but overall it is very nice. If you’re looking for a powerful, good-looking notebook computer, I recommend the HP dv6t Select Edition. Especially if you can find any special offers from HP (the coupon I used has expired, but they seem to do a lot of coupons, so look around if you’re considering buying from HP!)

And finally, here is a view of the bottom, which is black plastic rather than metal. I had a hard time finding bottom views when I was shopping for laptops, so hopefully this will be helpful for others:

Full Triple-J Laser Interview

June 7, 2010

Hey, remember when I was randomly interviewed by the Australian radio station triple j a few weeks ago as part of their feature on the 50th anniversary of the laser? Well, in their final broadcast they only used a couple of minutes but the original interview was fifteen minutes long. So, I contacted them and asked if I could have the full audio file, and after some digging, they found it and sent it to me!

So, if you’d like to hear me talk in more detail about the ChemCam instrument and MSL and how fun it is to shoot stuff with lasers, check out this mp3 file! (12 MB)

Thanks again to Kate and Irene at triple j for interviewing me and for providing the full audio file so that I could post it here!

Talking lasers on aussie radio

May 12, 2010

This is what my work is like every day. Honest.

Through a crazy random happenstance, I was just interviewed by a friend of a friend of a friend at Australian radio station ‘triple j‘ for a feature on lasers! We talked all about shooting stuff with lasers, why one might want to do that (other than because it’s awesome) and how the real lab is not quite what people picture.

The show is called Hack with Kate O’Toole, and it airs in about 2 hours at 1:30 pm AEST (11:30 pm EST). Update: I fail at time zones. The show aired at 5:30 AEST. It looks like you can listen to programs online for one week after they air, so no worries if you don’t see this in time, you should still be able to find it.

Update: You can download the show as a podcast at this link, or if that doesn’t work, try here. The feature on lasers starts at 18:22.

Sounds like they edited my interview a lot, basically just leaving the first stuff I talked about. But they also talked to some other laser folks, including a long interview about the LISA mission searching for gravitational waves, so I recommend you check it out.

Off to MarsSed 2010

April 17, 2010

I’m headed off to El Paso Texas tomorrow! Why? Because that’s where the Mars Sedimentology and Stratigraphy workshop is! I’ll be presenting my work on the Gale Crater landing site for MSL on tuesday and then the second part of the week will be a geology field trip to interesting and instructive locations. I’m really looking forward to it, since the best way to learn geology is to go out and see it in person. Check out the awesome field guide that JPL put together for the trip:

Frickin’ Laser Beams: Fact vs Fiction

February 8, 2010

Greetings OpenLab 2010 readers! This blog has moved! I am now blogging at: http://blogs.agu.org/martianchronicles/

Last month I spent a week out at Los Alamos National Laboratory vaporizing things with a high powered laser. Now, as I drown in data that I collected out there, I thought I’d take a moment to talk about lasers.

When I tell people that I zap things with lasers, I can almost see the mental images flickering behind their eyes. They tend to look something like this:

Man, I wish.

I hate to burst your bubble, but working with lasers, although very cool, is not as showy as most sci-fi depictions. To help understand why, let’s first talk about how lasers work.

The word laser is actually an acronym for Light Amplification by Stimulated Emission of Radiation, and that actually sums up how they work quite well. There are lots of different types of lasers these days but they all share a few common characteristics. First, you need the “lasing medium” – that is, the stuff that will give off the light. The first lasers used artificial ruby crystals, but now there are lasers that are based on everything from CO2 gas to organic dyes to various semiconductors. The laser I use for my research is a Nd: YAG which stands for Neodymium-doped Yttrium Aluminum Garnet crystal.

Ok, so we have a “lasing medium”, now we need to make it shine. Things give off light when they have electrons in high energy levels jumping back down to lower energies and getting rid of the excess energy as photons. In a laser, the goal is to get something called “population inversion”, meaning that there are more electrons in excited energy levels than there are in the ground state. This is typically done with a flash lamp in a process called “pumping“. By shining very intense light on the lasing medium, the electrons all get excited and the laser is ready to, well, lase.

Diagram of a ruby laser from HowStuffWorks.

Of course, the goal of a laser is to have a nice narrow beam, but if you just have a lump of stuff with excited electrons, the light will be given off in all directions. A fluorescent bulb is a good example of this. A lasing medium acts in much the same way, shining a diffuse light in all directions, unless we do something to it. The secret is to place it between two mirrors, one which reflects all light, and one which reflects only some of the light that hits it.

Initially, the atoms in the lasing medium give off light in all directions, but some of those photons will end up traveling along the laser, bouncing back and forth between the two mirrors. Here is where the laser really starts working. It turns out that when you have photons of a certain energy traveling along through a bunch of atoms with excited electrons that have the same energy, you get “stimulated emission“. The first photons cause the electrons to jump down and emit identical photons. And I do mean identical. Yes they have the same energy (and therefore the same frequency/wavelength/color), but the new photons also have the same phase, polarization and direction as the initial ones. They are completely indistinguishable at the quantum level.

As you might expect, this stimulated emission leads to a chain reaction. Each photon of laser light can stimulate new photons to join it. Since one end of the laser is partially transparent, the result is a narrow beam of light made up of identical photons: a frickin’ laser beam!

Wonderful. Now that we understand how they work, I want to address a few misconceptions about lasers in science fiction and popular culture in general.

1. Laser beams are visible.


With a laser, the idea is to have all of the light going in the same direction, right? That means that if you can see the laser beam from the side, as shown in this picture from Star Trek, and in pretty much every depiction of lasers ever, then something isn’t right! The light is being scattered out of the beam. If you’ve ever used a laser pointer you know that even though it gives off visible (usually red or green) light, you just see a dot where it is pointing. Now, if you shine it at someone who is smoking, or if you use it outside in the fog,  or in a dusty room, you can see the beam because the light is reflecting off of particles in the air (smoke or water droplets or dust).

So, yes sometimes visible lasers in air are plausible because there could be stuff in the way, but visible lasers in space? No way!

There are some other caveats to this also. Not all lasers use visible light! The Nd:YAG that I use for my research and the similar laser used by ChemCam emit infrared light. It is completely invisible, no matter what. This makes it incredibly dangerous to work with lasers like this, especially when first lining up the optics, because you can’t tell if the laser is being reflected around the room! Just because these lasers are not visible doesn’t mean they can’t destroy your retina in a millisecond, so we wear special protective goggles designed for the specific wavelength that the laser emits at all times when the laser is on.

Also: you can’t see the laser beam traveling from the source to the target. It’s going at the speed of light. So all those sci-fi depictions of laser blasts whizzing by the hero’s head like tracer bullets: wrong.*

*Yes, I know, some sci-fi explains this by invoking pulses of plasma and not actual lasers. That’s a whole different can of worms with its own issues. Suffice it to say that most people *think* those blasters, phasers, etc. are supposed to be lasers, so I’m debunking that misconception.

2. Pew pew pew!


That’s not what they sound like. I know. I’m sorry.

Low powered lasers don’t really sound like anything. And can you imagine how annoying it would be if they did? At the grocery store checkout: pew pew pew! Using a CD or DVD player: pew pew pew! Laser pointer: pew pew!

Yes, but the “pew pew” sound really comes from things like Star Wars, depicting lasers used as weapons. So what about big lasers, capable of vaporizing things? Nope. With higher powered lasers, at least the kind I work with, the main sound comes from the flash lamp. It’s sort of a ticking noise, one tick per flash, one flash per laser pulse. Now, when we crank up the power or use something called a “q-switch” to make each pulse shorter and more intense, you get another noise that comes from the laser actually vaporizing things. That noise is more of a “crack” or “pop” noise. In fact, I once popped some bubble wrap in the laser lab while my collaborators were aligning the laser and totally freaked them out because they thought it was the laser. Oops…

The popping noise is essentially the same thing as thunder: a rapidly expanding ball of plasma causes the air to be compressed in a shockwave. Our laser plasmas are tiny, so they just make a little noise. Lightning bolts (plasma formed by electrical discharge) are rather larger, and so is their noise. Many of my experiments are done zapping rocks inside a vacuum chamber, and it’s always fun to hear the noise fade away as we decrease the air pressure in the chamber.

3. Lasers as weapons.


They’re really not that great.

There are a lot of issues with using lasers as weapons. First of all: the optics. For a laser to be useful as a weapon, you would have to focus the light as tightly as possible on the target. De-focus at all, and you might still blind them, but there won’t be much vaporization going on. The precision required for the optics to do this makes a hand-held laser really impractical. The slightest bump or wiggle and all of a sudden your gun is a high-powered flashlight. There’s also the issue of air. Anyone who has looked through a telescope or out over a parking lot on a hot day has seen the shimmering mess that the air can make of an otherwise clear image. Now imagine trying to shine a tightly focused beam of light through that mess and hitting a target. Not an easy task. The military has worked on this to some extent with adaptive optics used for giant plane-mounted anti-missile laser, but it is a significant problem.

The air poses another problem: it absorbs light. In fact, a high enough powered laser can cause the air itself to break down into a ragged line of plasma. I’ve seen this in the lab and it is awesome. The problem is that plasma is full of free-flying electrons, so it absorbs light. A laser strong enough to use as a weapon would also be strong enough to turn the air to a plasma, which would then block the laser from hitting its target. One way around the plasma problem is to use a pulsed laser. As long as the pulses are timed so that the plasma has dissipated before the next pulse is fired, the plasma is not as much of a problem.

I mentioned lightning earlier and that’s relevant here. There is a way to make use of the “plasma issue”, because plasmas conduct electricity. So in theory it would be possible to use a laser as a long-distance taser! The laser would first create a conduit of plasma out of the air, and then with a high enough voltage, an electric shock could be send down the plasma to the target. This would not be a subtle weapon: at this point the lightning analogy is not really an analogy anymore. It would basically be a lightning gun, and would make a noise to match. I thought I was being really clever when I thought of this, but it turns out I’m not the first: the US military has experimented with them.

Another problem with lasers as weapons is the power source. It takes quite a lot of power to make a laser capable of doing damage, and it would probably not be practical for a person to carry such a power source around. I’m playing the video game “Fallout 3” right now, and the energy weapons use things called “microfusion cells” for ammunition. Right now, we don’t even have power-positive macro-fusion cells, so bullet-sized fusion powerplants are not available yet.

Finally, there is the issue of collateral damage. The thing with light is that it tends to reflect off of things. This means that anyone using a laser weapon better be wearing the appropriate protective eyewear or else their own target is going to blind them. Aside from the practical issues with blindness, the Geneva conventions also specifically forbid laser weapons that cause blindness (in other words, all of them).

In my opinion, I highly doubt that lasers will ever be practical as pistols or rifles. Maybe as large mounted guns on tanks or something. But really, the most likely place for lasers as a viable weapon is space. Without air, the difficulties with plasma creation and turbulence are removed. The issue of power and optics remain, but I could plausibly see a satellite or space station with the stability and power to use a laser as a weapon. It might still be difficult to focus on a distant target, just due to the physical limits on the optics, but the advantage of near-instant travel-time might be of benefit when you’re aiming at a target thousands of km away, traveling at thousands of km per hour.

Voting is fixed!

November 2, 2009

There were some issues with the voting widget on the University Science Writing competition, but they have been resolved, and it turns out it was counting the votes all along! So go vote for my post if you haven’t done so yet today! Don’t worry if you don’t see a number in the grey voting widget box. They decided to hide the number of votes from everyone except the authors.

Ans while you’re there, go ahead and check out and vote for other finalists too. There are some great other posts!

Edit: Can anyone else see the voting widget on my post? I just edited the voting instructions in the text to reflect the fact that they got rid of the visible number of votes, and when I saved, the widget disappeared.

voteforme